如果不包含函数列表，C++ 程序将无法编译

Question

我有 3 个文件，main.cpp、Graphics.cpp 和 Graphics.h。函数定义在 Graphics.h 中。这些函数位于 Graphics.cpp 中。主程序在 main.cpp 中。代码编译正常，但无法构建。

当我运行时

$ g++ -Wall -o "main" "main.cpp" -lSDL -lSDL_image -lSDL_mixer -lSDL_ttf               
/tmp/cce3Gqez.o: In function `main':
main.cpp:(.text+0xfd): undefined reference to `Graphics::clear(int, int, int)'
main.cpp:(.text+0x207): undefined reference to `Graphics::drawPixel(int, int, int, int, int)'
main.cpp:(.text+0x364): undefined reference to `Graphics::drawRect(int, int, int, int, int, int, int)'
main.cpp:(.text+0x4b7): undefined reference to `Graphics::fillRect(int, int, int, int, int, int, int)'
main.cpp:(.text+0x4c5): undefined reference to `Graphics::flip()'
/tmp/cce3Gqez.o: In function `InitProgram()':
main.cpp:(.text+0x54f): undefined reference to `Graphics::init(int, int, bool)'
collect2: error: ld returned 1 exit status

函数的引用没有被识别？当我在 main.cpp 的顶部包含“#include “Graphics.cpp””时，程序运行正常。我确信这样做是不合适的，但我无法让它以任何其他方式工作。 这是 3 个源文件:

#include "Graphics.h"
//#include "Graphics.cpp"

const int FPS = 30;
const int FRAME_TIME = 1000/FPS;
const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;
const int FULLSCREEN = false;

Graphics graphics;

bool InitProgram();
void FreeProgram();
bool ProgramRunning();

int main(int argc, char *argv[])
{
    if(!InitProgram())
    {
        FreeProgram();
        return false;
    }

    int counter = 0;

    while(ProgramRunning())
    {
        int frameStart = SDL_GetTicks();

        counter++;

        if(counter > 90)
        {
            counter = 0;
            graphics.clear(rand()%255, rand()%255, rand()%255);
        }

        for(int i = 0; i < 100; i++)
            graphics.drawPixel(rand()%SCREEN_WIDTH, rand()%SCREEN_HEIGHT, rand()%255, rand()%255, rand()%255);

        graphics.drawRect(rand()%SCREEN_WIDTH, rand()%SCREEN_HEIGHT, rand()%100, rand()%100, rand()%255, rand()%255, rand()%255);
        graphics.fillRect(rand()%SCREEN_WIDTH, rand()%SCREEN_HEIGHT, rand()%100, rand()%100, rand()%255, rand()%255, rand()%255);

        graphics.flip();

        int frameTime = SDL_GetTicks()-frameStart;
        int delay = FRAME_TIME - frameTime;

        if(delay > 0)
            SDL_Delay(delay);
    }

    FreeProgram();

    return 0;
}

bool InitProgram()
{
    if(SDL_Init( SDL_INIT_EVERYTHING) == -1)
        return false;

    if(!graphics.init(SCREEN_WIDTH, SCREEN_HEIGHT, FULLSCREEN))
        return false;

    SDL_WM_SetCaption("Graphics Test", NULL);

    return true;
}

void FreeProgram()
{
    SDL_Quit();
}

bool ProgramRunning()
{
    SDL_Event event;

    while(SDL_PollEvent(&event))
    {
        if(event.type == SDL_QUIT)
            return false;
    }

    return true;
}

我该怎么做才能正确编译？我缺少链接器标志吗？我正在使用 g++，我是编写头文件的新手。编译 main.cpp 的正确方法是什么。

Answer 1

您不应该使用预处理器来#include cpp 源文件(*.cpp)。

您必须链接 Graphics.cpp 或从它编译的目标文件。

试试这个:

$ g++ -Wall -o "main" "main.cpp" "Graphics.cpp" -lSDL -lSDL_image -lSDL_mixer -lSDL_ttf